Development of the electronics industry has been accompanied by sharp demand for printed-circuit boards for mounting electronic devices thereon, such as ICs (integrated circuits) and LSIs (large-scale integrated circuits). Manufacturers have attempted to realize small-size, lightweight, and high-function electronic equipment, which has long been desired. To this end, manufactures have recently come to employ mounting methods making use of a film carrier tape, such as a TAB (tape automated bonding) tape, a T-BGA (ball grid array) tape, an ASIC tape, or an FPC (flexible printed circuit). Use of film carrier tapes for mounting electronic devices thereon has become of increasing importance, especially for manufacturers of personal computers, cellular phones, and other electronic equipment employing a liquid crystal display (LCD) that must have high resolution and flatness, as well as a narrow screen-frame area.
In addition, in order to attain higher-density mounting on a narrower space, IC chips have been mounted on an insulating layer of a flexible printed wiring board. Such a product is called COF (chip-on-film).
Since the flexible printed wiring board serving as a substrate of COFs does not have a device hole, a laminate film obtained by laminating in advance a conductor layer and an insulating layer is employed. When IC chips are mounted directly on the wiring pattern, positioning is performed on the basis of marks such as an inner lead and a positioning mark which are visible from the insulating layer, followed by joining the IC chips and the wiring pattern; i.e., the inner lead, by means of a heating tool (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2002-289651, FIGS. 4 to 6 and paragraphs [0004] and [0005]).
Such a semiconductor chip is mounted while the insulating layer thereof is in direct contact with a heating tool. Since the insulating layer is heated to a considerably high temperature by the heating tool during the course of mounting, a portion of the insulating layer is caused to adhere to the heating tool by melting, thereby causing stoppage of a production apparatus. In addition, unfavorable deformation of the carrier tape occurs. In the case where the insulating layer is melt-adhered to the heating tool, the heating tool is stained, thereby deteriorating reliability and productivity.
Such melt adhesion to the heating tool is critical when semiconductor chips are mounted on a COF film carrier tape or a COF FPC having no device hole.
The present invention has been made to solve the aforementioned problems, and an object of the present invention is to provide a releasing layer transfer film which can form, in a simple manner, a releasing layer on a COF flexible printed wiring board, the releasing layer preventing melt adhesion of an insulating layer to a heating tool, thereby enhancing productivity and reliability of semiconductor devices produced by use of a semiconductor chip mounting line.